1. Field of the Invention
The present invention relates to a valve system for an engine, including a valve resting mechanism provided between an engine valve and a valve lifter supported by a cylinder head so as to be slidably driven by a valve system cam. The valve resting mechanism is capable of switching an acting state and a non-acting state of a pressing force applied from the valve lifter to the engine valve in the valve opening direction and turning, in the non-acting state of the pressing force, the engine valve into the resting state irrespective of the sliding motion of the valve lifter.
2. Related Art
A valve system of this type has been known, for example, from Japanese Utility Model Publication No. Hei 3-7526. In a valve resting mechanism of the valve system disclosed in this document, a slide pin having a containing hole capable of containing the leading end of a valve stem of an engine valve is directly fitted in a valve lifter supported in a cylinder head so as to be slidably driven by a valve system cam. The rotation of the slide pin around its axis is prevented by fitting the leading end of the valve stem in a groove formed in a pin holder.
The above valve resting mechanism, however, has a disadvantage: The rotation stop of the slide pin is achieved in a state in which the valve resting mechanism is assembled in the valve stem of the engine valve. In other words, the rotation stop of the slide pin with respect to the valve lifter is not achieved in the step of assembling the valve resting mechanism. As a result, it is difficult to align the groove of the pin holder with the leading end of the valve stem upon assembly of the valve lifter in the cylinder head. This complicates the step of assembling the valve resting mechanism.
In view of the foregoing, an object of the present invention is to provide a valve system for an engine valve which facilitates the work of assembling a valve resting mechanism.
To achieve the above object, there is provided a valve system for an engine including an engine valve including a valve body capable of opening/closing a valve port provided in a cylinder head so as to be opened to a combustion chamber, and a valve stem whose base end is integrated with the valve body, the engine valve being openably/closably supported in the cylinder head so as to be spring-biased in the direction of closing the valve port. A valve lifter is supported in the cylinder head so as to be slidable in the same axial direction as the axis of the valve stem. A valve resting mechanism is provided between the valve lifter and the engine valve, the valve resting mechanism being capable of switching an acting state and a non-acting state of a pressing force applied from the valve lifter to the engine valve in the valve opening direction and turning, in the non-acting state of the pressing force, the engine valve into the resting state irrespective of the sliding motion of the valve lifter.
In this valve system, the valve resting mechanism includes a pin holder slidably fitted in the valve lifter formed into a bottomed cylinder shape with its end on the valve system cam closed. The pin holder has a sliding hole having an axis perpendicular to the axis of the valve lifter, and an insertion hole opened in the inner surface of the sliding hole so as to allow the valve stem to be movably inserted therethrough in the axial direction. A slide pin is slidably fitted in the sliding hole with its one end facing to an hydraulic chamber, the slide pin having a containing hole coaxially connectable to the insertion hole. A return spring is included for biasing the slide pin in the direction of reducing the volume of the hydraulic chamber. A rotation stopping means is provided between the pin holder and the slide pin for stopping the rotation of the slide pin around its axis. The slide pin is fitted in the sliding hole so as to be slidable between a position wherein the containing hole is coaxially aligned to the insertion hole for allowing the leading end of the valve stem to be contained in the containing hole, and a position wherein the leading end of the valve stem is brought into contact with the outer side surface of the slide pin.
With this configuration, when the slide pin is moved to the position wherein the containing hole is coaxially aligned to the insertion hole of the pin holder, the pin holder and the slide pin are moved, together with the valve lift, to the engine valve side due to the sliding motion of the valve lifter by a pressing force applied from the valve system cam. However, only the leading end of the valve stem inserted in the insertion hole is contained in the containing hole and the pressing force in the valve opening direction is not applied from the valve lifter and the pin holder to the engine valve. The result is that the engine valve remains rested.
When the slide pin is moved to the position wherein the outer side surface is brought into contact with the leading end of the valve stem, the pressing force in the valve opening direction is applied to the engine valve along with the movement of the pin holder and the slide pin toward the engine valve due to the sliding motion of the valve lifter by the pressing force applied from the valve system cam. The result is that the engine valve is operated to be opened/closed in accordance with the rotation of the valve system cam. Also, since the rotation of the slide pin around its axis in the pin holder is prevented by the rotation stopping means, the valve resting mechanism can be easily assembled to the valve stem by mounting the valve lifter to the cylinder head in a state that the pin holder in which the slide pin has been fitted is fitted in the valve lifter.
The rotation stopping means can be a stopper pin mounted in the pin holder so as to pass through the slide pin, while permitting the movement of the slide pin in the axial direction. With this configuration, the rotation stopping means can be simplified.
The pin holder can have an extension hole capable of containing the leading end of the valve stem, the extension hole being coaxial with the insertion hole with the sliding hole put between the insertion hole and the extension hole. A shim for blocking an end portion of the extension hole on the closed end side of the valve lifter can be mounted on the pin holder so as to be allowed to be brought into contact with the closed end of the valve lifter.
Because the leading end of the valve stem is contained not only in the containing hole but also in the extension hole in the valve resting state, it is possible to reduce the length of the containing hole, that is, the diameter of the slide pin, and hence to miniaturize the pin holder and further miniaturize the valve resting mechanism as a whole. Further, it is required to block the end portion of the extension hole on the closed end side of the valve lifter for applying a pressing force from the valve lifter to the pin holder, and according to this invention, the end portion of the extension hole is blocked with the shim brought into contact with the closed end of the valve lifter Accordingly, it is possible to simplify the structure of the pin holder, and to suitably adjust a gap at the valve head of the engine valve by changing the thickness of the shim.
A containing cylinder portion coaxial with the axis of the extension hole can be integrally provided on the pin holder at a position facing to the closed end of the valve lifter, and the shim formed into a disk shape is partially fitted in the containing cylinder portion. With this configuration, it is possible to simply mount a relatively small shim on the pin holder.
A projecting portion to be in contact with the shim is integrally provided on the inner surface of the closed end of the valve lifter. With this configuration, the sliding motion of the valve lifter with respect to the cylinder head can be reliably performed along the axis of the valve stem so that the pressing force is applied from the valve lifter to the pin holder on the extension of the axis of the valve stem of the engine valve. As a result, the sliding motion of the valve lifter can be smoothened.
A coil spring for biasing the pin holder toward the closed end of the valve lifter can be provided between the pin holder and the cylinder head so as to surround the valve stem at a position wherein the outer periphery of the coil spring is not in contact with the inner surface of the valve lifter; and positioning portions for positioning an end portion of the coil spring in the direction perpendicular to the axis of the valve stem are provided on the pin holder. With this configuration, it is possible to reliably apply the spring force of the coil spring along the axis of the valve stem, and to prevent the occurrence of a frictional loss due to the slide-contact of the outer periphery of the coil spring with the valve lifter.
Positioning portions are projections integrally provided on the pin holder, and the projecting amount of each of the projections is less than the diameter of the coil spring. The positioning portions can be grooves provided in the pin holder, the depth of each of the grooves being less than the diameter of the coil spring. Even if the coil spring is contracted, it is not in slide-contact with the pin holder. As a result, it is possible to prevent the occurrence of the frictional loss due to the slide-contact of the coil spring with the pin holder.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.